The present invention relates to a method of forming a fine pattern in production of semiconductor equipment. Further the present invention relates to a process for preparing a fluorine-containing polymer for a resist which is used in forming a fine pattern.
Ultra fine fabrication is required for various electronic parts such as semiconductor integrated circuit, and a resist is widely used for a processing technology therefor. With the pursuit of multi functions and high density of electronic parts, ultra fine fabrication of a resist pattern to be formed is demanded. As the resist used for fabrication of such an ultra fine pattern, there are, for example, chemically amplifying resists disclosed in JP63-27829A, etc.
A chemically amplifying positive resist is, for example, a composition comprising a photoacid generator and a resin being soluble in a developing solution and having an alkali soluble group (—COOH group, —OH group, etc.), in which a group (protective group) having a dissolution inhibiting effect is introduced. In an un-exposed state, solubility in a developing solution (2.38% aqueous solution of tetramethylammonium hydroxide) is inhibited by the protective group.
When the resist film formed on a substrate is irradiated with light, X-ray, high energy electron beam or the like, a photoacid generator is decomposed at an exposed portion and an acid is generated and when the resist film is further subjected to heat-treating after the exposure, the acid acts as a catalyst to convert a protective group to an alkali soluble group. Therefore an intended pattern can be formed by dissolving and removing, with a developing solution, the exposed portion in which the protective group has been decomposed.
For forming a pattern using such a resist, a reduction projection exposure system usually called a stepper is generally used as an exposure system. As a result of a recent remarkable progress of multi functions and high density of electronic parts, a further fine circuit is demanded, which makes it necessary to form a fine pattern.
In the above-mentioned exposure system, since a pattern fabrication is carried out by projecting an optical image on a substrate, a limit of resolution depends on a wavelength of light used for the exposing.
For the fine fabrication, a wavelength of light source used for the exposing has been shortened. It is a matter of certainty that in production of a device coming after a giga bit memory era, F2 laser having a wavelength of 157 nm will be mainly used as light source. Therefore, development of a chemically amplifying resist capable of forming a fine pattern using F2 laser as light source has already been initiated.
However materials which have been used for conventional resist absorbs a large amount of F2 laser having a wavelength of 157 nm. When F2 laser is used for the exposing of a photosensitive composition prepared from such materials, sufficient amount of exposure light does not reach the bottom of the resist. Therefore uniform exposing in the direction of a depth of the photosensitive composition formed on the substrate cannot be carried out, and it is difficult to enhance resolution.
Various fluorine-containing polymers having a norbornene backbone have been studied as a resist polymer being excellent in transparency to F2 laser. For example, in International Publication Nos. WO00/67072, WO03/006413 and WO03/007080, there are proposed fluorine-containing polymers prepared by copolymerizing norbornene derivatives having a functional group:
and a functional group:
having the protected OH group. The synthesis of the fluorine-containing polymer having those protective groups is carried out by copolymerization after previously preparing a norbornene derivative having a group:

However though a resist film obtained from a resist composition comprising a fluorine-containing polymer having a structural unit derived from a norbornene derivative having a protective group introduced by a conventional method is excellent in transparency, there is a problem that when formation of a fine resist pattern is intended, sufficient resolution is difficult to obtain because solubility in a developing solution of the fluorine-containing polymer, in which the protective group has been decomposed by an acid generated from a photoacid generator at exposing, is insufficient.
The present invention was made based on new findings to solve the mentioned problems. An object of the present invention is to provide a method of forming a fine pattern by using, as a resist, a highly practicable fluorine-containing polymer which can undergo resolution of fine pattern and is highly transparent to exposure light having a short wavelength such as F2 excimer laser.